Measuring instrument for determining the scattering and absorption coefficient of the atmosphere

Abstract

A measuring instrument for simultaneous in situ determination of the spectral scatting and absorption coefficient, which can also be called an extinction meter, has a modulated light source and an optical system encompassing the hemisphere; the optical system has a multiply folded ray path with a focal point in the volume to be measured, and through this system the measurement signal is projected to detectors. The scattering measurement signals, which are maximally enlarged in this way, are then separated from those for the absorption. The extinction meter also has not only an integrating nephelometer for monitoring purposes but also a transmission meter for low transmission factors. Because of the small three-dimensional size and the streamlined shape of the measuring portion of the extinction meter, the extinction meter can be carried in aircraft and surface vehicles. Because of the disposition of the optical system, the error in the measurement values is negligible, in comparison with other instruments with which only the scattering coefficient can be determined. Moreover, the calibration value during a measurement phase can be determined both automatically and manually. Contamination of the instrument with gas to be measured is reduced, by the stabilization of a turbulence ring by means of baffles. Moreover, interference with the flowing aerosol on the part of the instrument is largely eliminated via a hoop-like hood functioning like a wing-tip slot.

What is claimed is: 
     
       1. A measuring instrument for determining the scattering and absorption coefficient of the atmosphere, comprising: an emitter side comprising a light emitter having a light source which is a pulsed laser, and a device for varying the frequency associated with the laser;   an annular mirror (5) having an inlet slit (5a) and a first diametrically opposed outlet slit (5b) for the introduction and exiting of aerosol gas to be measured;   a receiver side having alight detector (27) and a sound detector (22') for receiving emitter light attenuated in the atmosphere;   a rotationally symmetrical ellipsoidal mirror (10) disposed such that a first focal point (6) of the ellipsoidal mirror is located in a substantially center point of a substantially center plane of the annular mirror (5) and a second focal point is located in a substantially middle position of the light detector (21) and the sound detector (22') associated with the light detector (21), and   wherein the light detector and the sound detector (22') are accommodated in a fluidicly shaped space, so that radiation of small divergence emitted by the light emitter is reflected a multiplicity of times, after introduction thereof into the annular mirror (5), ray segments of light reflected by the annular mirror interest concentrically about the first focal point (6) of the ellipsoidal mirror (10), and the attenuating gas to be measured are carried, via the first focal point (6) from the inlet (5a) slit to the first outlet slit (5b).   
     
     
       2. An instrument as defined by claim 1, further comprising: a frustoconical housing 18 surrounding the fluidicly shaped space;   a resonance absorber (23) securing the sound detector (22') to a bottom surface (18') of the frustoconical housing (18), and   wherein the light detector (21) is secured in a sound-conducting manner on the sound detector (22').   
     
     
       3. An instrument as defined by claim 1, further comprising: a first perforated plate (2a) and a beam splitter (2b) for dividing radiation emitted by the laser or laser diode, said beam splitter (26) being of a low transmission and high reflection;   a first optical detector (3) disposed downstream in the radiation direction with respect to the beam splitter (2b) for detecting one part of the laser radiation;   a second perforated plate (5c) disposed in the annular mirror (5) through which (5c) another part of the radiation passes;   a second optical detector, disposed down-stream in the radial direction of the annular mirror (5) to a second outlet slit (5d) in the annular mirror;   wherein the another part of the radiation is formed into a beam and directed downstream after n reflections in the annular mirror (5); and after exiting through the second outlet slit (5d) in the annular mirror (5) toward the second optical detector (7), which detector (7) forms an angle with an axis of the beam.   
     
     
       4. An instrument as defined by claim 1, wherein an inside surface of the circular annular mirror (5'), symmetrically to its center face, has a curvature on the order of magnitude of the annular mirror diameter, the annular mirror diameter is greater than the diameter of the ellipsoidal mirror (10'), and an edge of the ellipsoidal mirror above the surface of the annular mirror 5 is embodied as a double light trap (17), so as to suppress interfering radiation arriving diffusely from the annular mirror (5') and reflected via the ellipsoidal mirror (10') to the light detector (21). 
     
     
       5. An instrument as defined by claim 1, further comprising a calibration (9) standard disposed between a second outlet slit (5d) in the annular mirror (5) and the second optical detector (7) and having an optical and acoustical scattering body as a reflector, the calibration standard being positionable by means of a solenoid behind the outlet slit precisely in such a way that the arriving pulsed radiation is defined and reflected with a distribution approximately in accordance with Lambert's law, and the proportion of the absorbed radiation that is partly converted into acoustical radiation is correspondingly projected in a defined manner via the second outlet slit (5d), with a distribution of energy approximately in accordance with Lambert's law, onto the opposite rim of the ellipsoidal mirror (10) and from there is reflected to the second focal point thereof. 
     
     
       6. An instrument as defined by claim 1, wherein the upper part of the measuring instrument (100) is embodied in streamlined fashion, further comprising an inlet nozzle (11) that is black on the inside and widens conically toward the annular mirror (5) for introducing the provided on an outside of the inlet slit (5a) in the annular mirror (5), and an outlet nozzle (12), which is likewise black on the inside and widens conically toward the outside, provided on the outside of the first outlet slit (5b) diametrically opposite the inlet slit (5a), an upper housing (19) having a part which tapers to a flat shape covering the outlet nozzle (12), a hoop-like hood (13) functioning like wing-tip slot embodied near an end of the upper housing part (19') tapering to a flat shape for the aspiration of the gas flowing through the outlet nozzle (12). 
     
     
       7. An instrument as defined by claim 1, further comprising: a hollow sphere (15) for closing off the fluidic shaped space in the interior of the frustoconical housing via the bottom surface (18') thereof, said hollow sphere (15) being highly absorbent on the inside and having a low coefficient of adhesion, the sphere 15 having a recess for receiving the detectors (21, 22') attached to the housing bottom (18') and opposite the recess (15') merging with an absorbing, straight truncated cone having a low coefficient of adhesion;   crescent-shaped, approximately semicircular baffles (14) protruding from the cone tapering inward at ends thereof, and   wherein the baffles (14) having their greatest projection at right angles to a connecting line between the inlet and outlet nozzles (12) and are oriented inclined toward the first focal point (6), and in the direction of the outlet nozzle (12) the baffles rise by a few angular degrees with respect to the straight connecting line between the inlet (11) and outlet nozzles (12).   
     
     
       8. An instrument as defined by claim 1, wherein the inside of the ellipsoidal mirror, the annular mirror and the beam splitter are heatable in such a manner that their temperature always remains somewhat above the temperature of the ambient air, and the detectors and the light source are designed in temperature-stabilized fashion. 
     
     
       9. An instrument as defined by claim 1, further comprising: a transparent, acoustical resonance means (41) disposed upstream of the light detector (21) in the path of a sound pulse reflected from one focal point to the other of the ellipsoidal mirror (10), the resonance body being filled with a liquid or a dispersion;   a monochromatic light source (31), a condenser lens (32), a diaphragm (33) forming an optical gap and a lens (34) disposed in that order in the light propagation direction approximately at right angles to the center axis of a sound formed by the acoustical pulse, on one side of the resonance body (41);   a light trap (38) and a collecting lens (39) with a following light detector (40) disposed on the opposite, other side of the resonance body in the primary axis of the lens (34), and   wherein the primary axis of the lens and the primary axis of the collecting lens form a very small angle, and the spacing between the resonance body (41) and the light trap (38) is substantially greater than the spacing between the resonance body (41) and the lens (34).   
     
     
       10. An instrument as defined by claim 9, further comprising a third optical detector (36) disposed below a second beam splitter (35) provided between the lens (34) and the resonance body (41) for measuring the constancy of the light source (31), and a second light trap (37) associated with the second beam splitter (35) and the third optical detector (36) for radiation limitation. 
     
     
       11. An instrument as defined by claim 9, wherein the transparent, acoustical resonance body comprises a resonance housing (44) for gases or liquids provided with side windows both in the direction toward the lens (34) and in the direction toward the collecting lens (39), and a transparent cover plate (43) on the side remote from the light detector (27), the spacing of which with respect to the light detector (21) being finely adjustable. 
     
     
       12. An instrument as defined by claim 1, further comprising an optical-acoustical beam splitter plate (45) oriented at substantially 45° from the center axis of the radiation is provided above the detector (21') retained on the housing bottom (18'), the optical and acoustical radiation vertically incident upon the detector (21) being distributed by the beam splitter plate (45) to the detector and a second detector. 
     
     
       13. An instrument as defined by claim 12, wherein the beam splitter plate (45) is a lightweight, thin, mirrored plastic plate having a low sound wave resistance, and the detector (21) is a sound detector and the second detector (40') is a light detector. 
     
     
       14. An instrument as defined by claim 12, wherein the beam splitter plate is a heavy glass plate (42) with a reflection-reducing coating, and the detector is a light detector and the second detector is a sound detector. 
     
     
       15. An instrument as defined by claim 12, wherein the beam splitter plate (45) comprises an opto-acoustical beam splitter cube comprising an upper prism (46) and a lower prism (47). 
     
     
       16. An instrument as defined by claim 15, wherein as soon as the sound wave resistance of the two prisms (46), (47) is approximately identical, the difference in the optical indexes of refraction is selected such that total reflection occurs at the lower prism (47). 
     
     
       17. An instrument as defined by claim 15, wherein as soon as the optical indexes of refraction are identical, the difference in the acoustical indexes of refraction is selected such that for the acoustical wave at the lower prism (47) having an acoustically lightweight medium, total reflection occurs. 
     
     
       18. An instrument as defined by claim 1, further comprising a transparent acoustical resonance plate (41') is disposed upstream of the optical detector (21) parallel to and spaced slightly apart therefrom, the resonance plate (41) having an optical reflection-reducing coating and being connected at one narrow end in a sound-conducting manner to the sound detector (40'). 
     
     
       19. An instrument as defined by claim 18, wherein the transparent acoustical resonance plate (41') is embodied in two halves, and the trapped air, as a resonator, is connected to the sound detector. 
     
     
       20. An instrument as defined by claim 1, wherein the sound detector (40') is attached in a sound-conducting manner to the side of the light detector (21), and is secured at the back, via a resonance absorber, to the frustoconical housing.